Optical switching element and image display device

ABSTRACT

The present invention provides an optical switching element causing less loss of light and permitting high response, thinning of an optical system for illumination, and the realization of an image display device exhibiting precise grayscale properties. In the optical switching element, an extraction surface of a light extraction unit mounted to a thin film is brought into contact with the total reflection surface of a light guide serving as a light guide unit comprising a glass plate or the like for transmitting light by total reflection, or near at a distance from the total reflection, surface for allowing extraction of evanescent waves, to extract the incident light transmitted through the light guide and emit the extracted light to the outside through an emission member. Such optical switching permits the light extract unit to be operated in a range of approximately a wavelength or half a wavelength, thereby providing an optical switching element capable of high-speed operation and having high contrast because the incident light does not leak due to total reflection during an off time.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The present invention relates to an optical switching element(light valve) used for optical communication and optical computation.The invention also relates to an optical switching element used in anoptical storage device, an optical printer, an image display device,etc., and particularly in an image display device.

[0003] 2. Description of Related Art

[0004] A conventional optical switching element comprises a liquidcrystal. As shown in a schematic configuration of FIG. 16, aconventional optical switching element 900 comprises polarizers 901 and908, glass plates 902 and 903, transparent electrodes 904 and 905, and aliquid crystal 906 or 907, so that when a voltage is applied between thetransparent electrodes, the direction of liquid crystal molecules ischanged to rotate the surface of polarization, resulting in opticalswitching. A conventional image display device comprises a liquidcrystal panel having such optical switching elements (liquid crystalcells) arranged in a two-dimensional form, in which the direction ofliquid-crystal molecules is controlled by adjusting the applied voltageto achieve grayscale.

[0005] However, a liquid crystal has low responsiveness, and is operatedat a response speed of only several milliseconds. Therefore, it isdifficult to apply an optical switching element comprising a liquidcrystal to optical communication, optical computation, an optical memorydevice such as hologram memory, an optical printer, and the like. Also,an optical switching element comprising a liquid crystal is subject tothe problem that the utilization efficiency of light deteriorates due topolarizers.

[0006] Higher image quality has recently been demanded in image displaydevices, and thus there has been a demand for an optical switchingelement which permits more precise display of grayscale than an opticalswitching element using a liquid crystal.

SUMMARY OF THE INVENTION

[0007] Accordingly, an object of the present invention is to provide anoptical switching element which permits high speed response with lowloss of light. Another object of the invention is to provide an imagedisplay device which can be relatively simply manufactured with highyield, and which permits color display with high resolution at low cost.A further object of the present invention is to provide an image displaydevice which permits thinning of an optical system for illumination andwhich has precise grayscale characteristics.

[0008] In order to achieve the objects, the present invention providesan optical switching element comprising a light guide which permitsextraction of light when a transmissive extraction surface is broughtinto contact with the light guide, and extraction of leaking evanescentlight when the extraction surface is brought near the light guide at adistance of half a wavelength, preferably ¼ wavelength, therefrom,whereby light can be turned on and off at high speed by finely moving alight extraction unit provided with the extraction surface for about awavelength or less. Namely, in accordance with the optical switchingelement of the present invention, the light guide has a total reflectionsurface capable of transmitting light by total reflection, and the lightextraction unit has the transmissive extraction surface which can bemoved between a first position at not more than the extraction distancefrom the total reflection surface, where evanescent light leaks, and asecond position at not less than the extraction distance therefrom.Since the optical switching element is capable of extracting evanescentlight, it does not necessarily require adhesion (close contact) to thetotal reflection surface of the light guide, and exhibits highreliability. An off state is caused by movement from the first positionto the second position at a distance of about a wavelength from thetotal reflection surface, and it is thus possible to provide an opticalswitching element which can be operated at high speed. Also, in the offstate, light from the light guide is totally reflected without leaking,and thus an optical switching element having high contrast can beprovided.

[0009] In the optical switching element, the light extracted by theextraction surface may be appropriately processed by an emission memberso that the light can be output to the outside, thereby permittingon-off operations. For example, at least one of an emission surface anda reflection surface at a different angle from the total reflectionsurface may be provided on the emission member so that the lightextracted by the light extraction unit can be output to the outside. Assuch an emission member, a micro prism or micro lens can be used forefficiently outputting the light extracted by the extraction surface tothe outside. As the emission member, it is possible to use an opticalelement having the shape of a truncated cone or truncated pyramid whichexpands in the emission direction. The use of such an optical elementenables a further increase in the efficiency of light extraction, andthe direction of the extracted light to be close to the directionperpendicular to the total reflection surface of the light guide.

[0010] Also a light scattering body can be used as the emission memberso that the extracted light can be emitted to the outside by scatteringby the emission member. Further, as the emission member, a member whichcan emit light by extracted light, for example, a member which usesultraviolet light as light to be transmitted to the light guide unit,and which contains a fluorescent agent emitting light when theultraviolet light is applied thereto, can be used.

[0011] Further, an optical switching element can be provided in whichwavelength selectivity is imparted to the light extraction unit todevelop different colors. For this purpose, the extraction surface orthe emission member may be provided to function as a color filter, amaterial having wavelength selectivity may be used as a scatteringmaterial or a light emitting agent.

[0012] The light extraction unit may be a transmissive type in whichextracted light is guided to the side opposite to the extractionsurface. Such a transmissive extraction unit is disposed on the lightemission side with respect to the light guide unit to function as anoptical switching element. On the other hand, the light extraction unitmay be a reflective type in which extracted light is guided to theextraction surface side, and such a reflective light extraction unit isdisposed on the side opposite to the light emission side with respect tothe light guide unit to function as an optical switching element. Alsothe light extraction unit may be an emissive type which emits light bythe light extracted by the extraction surface. In cases where theextracted light is scattered, or the light emitted by extracted light isemitted, a light absorbing layer is disposed on the side opposite to theemission side with respect to the light guide unit to absorb extraneouslight, thereby improving contrast.

[0013] Further, a non-movable light processing unit may be provided onthe emission side where the light extracted by the light extraction unitis emitted, and provided with a wavefront converting function, awavelength selecting function or a light emitting or scattering functionin place of the emission member having a scattering or wavelengthselecting function and provided on the light extraction unit forswitching operations. By providing such a light processing unit, it ispossible to simplify the configuration of the light extraction unit,facilitate movement due to a decrease in the operation load, and enablehigh-speed switching operations.

[0014] In such an optical switching element, the light extraction unitmay be separately supported so that it can be moved at a proper distancefrom the light guide. Where a thin film is laminated on the light guidewith spacers therebetween, and the light extraction unit is supported bythe thin film, it is possible to maintain an appropriate distance fromthe light guide, and unitize the light extraction unit. In the case ofthe transmissive light extraction unit, the light extraction unit can besupported by using a transmissive thin film laminated on the emissionside through spacers. In the case of the reflective light extractionunit, the extracted light can be reflected by a reflective thin filmlaminated on the side opposite to the emission side through spacers.Also a reflective or non-transmissive thin film may be used forpreventing extraneous light, thereby increasing a contrast.

[0015] In the optical switching element in which the light extractionunit is supported by a thin film, the light extraction unit supported bythe thin film may be driven by using an appropriate driving mechanism tooperate as a switching element. By providing a driving unit capable ofdriving directly or indirectly the light extraction unit supported bythe thin film in the optical switching element, it is possible toprovide the optical switching element with the driving mechanismintegrated therein. As such a driving mechanism, an element having apiezoelectric conversion function, such as a piezo element or the like,may be used; however, the light extraction unit may be electrostaticallydriven by the driving unit so that electrostatic attraction or repulsioncan be used, and a micro machine can be realized by using a thin filmtechnique. This permits a thin type to be formed with a simplemechanism, and improves productivity. Therefore, a small opticalswitching element can be provided at low cost. For example, atransparent electrode can be provided on the total reflection surface,and an electrode opposite to this electrode can be provided so that theoptical switching element can freely be controlled by applying a voltagethereto.

[0016] In the optical switching element in which the light extractionunit is supported by the thin film and electrostatically driven, thetransparent electrode is preferably disposed on the light guide sidewith respect to the emission member for emitting light by opticallyprocessing the light extracted by the extraction surface. This candecrease the distance between the transparent electrode provided on thetotal reflection surface and the transparent electrode provided on thethin film side, and drive the optical switching element with a lowdriving voltage. When the thin film is made of silicon, electrostaticthermal junction to glass spacers can be made. The use of electrostaticthermal junction requires no adhesive layer, and thus furtherfacilitates assembly in which the distance between the thin film and thetotal reflection surface is kept constant. Each of the spacers fordefining the distance between the thin film and the total reflectionsurface has a prismatic form so as to support the light extraction unitat each of four positions around, thereby minimizing the arrangementspace of the spacers, and securing the extraction surface having a widearea

[0017] Where a plurality of optical switching elements in accordancewith the present invention are used and arranged in a two-dimensionalform, and the light guide is connected thereto so that light can betransmitted, an image display device capable of two-dimensional displaycan be realized. The image display device has a high response speed andcan be operated at high speed, and can provide an image with a highcontrast. The image display device can also express grayscale in a timedivision manner by utilizing the high-speed properties of the switchingelements, and thus obtain a high quality image. Since light intensity isnot decreased by a polarizing filter or the like, and light is extracteddirectly from the light guide, the image display device capable ofdisplaying a bright image can be provided.

[0018] In such an image display device, the light extraction units aresupported by the thin film laminated on the light guide through spacers,thereby making the device thin and small. In order to electrostaticallydrive each of the optical switching elements arranged in atwo-dimensional form, it is possible to use a scanning electrode and asub-scanning electrode perpendicular to the scanning electrode. Theseelectrodes are disposed on the light guide and the thin film or thelight extraction units so that an image can be displayed by driving eachof the optical switching elements arranged in a two-dimensional form.

[0019] Also color display can be realized by imparting wavelengthselectivity to the light extraction unit. Further, a light sourcecapable of supplying light of the primary colors to the light guide in atime division manner can be used for permitting color display bysynchronously controlling the respective optical switching elements.Therefore, the image display device of the present invention has theeffect of obtaining a high quality color image and enabling thinning ofthe device.

BRIEF DESCRIPTION OF THE DRAWINGS

[0020]FIG. 1 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 1 of thepresent invention;

[0021]FIG. 2 is a graph showing the transmittance of evanescent wavesagainst the distance;

[0022]FIG. 3 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 2 of thepresent invention;

[0023]FIG. 4 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 3 of thepresent invention;

[0024]FIG. 5 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 4 of thepresent invention;

[0025]FIG. 6 is a drawing schematically illustrating the configurationof a an optical switching element in accordance with embodiment 5 of thepresent invention;

[0026]FIG. 7 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 6 of thepresent invention;

[0027]FIG. 8 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 7 of thepresent invention;

[0028]FIG. 9 is a drawing schematically illustrating the configurationof an optical switching element in accordance with embodiment 8 of thepresent invention;

[0029]FIG. 10 is a drawing illustrating a state in which an imagedisplay device in accordance with embodiment 9 of the present inventionis applied to a projection device;

[0030]FIG. 11 is a drawing illustrating the schematic configuration ofthe image display device shown in FIG. 10;

[0031]FIG. 12 is a partially cut-away perspective view illustrating theimage display device shown in FIG. 10;

[0032]FIG. 13 is a drawing illustrating another example in which animage display device in accordance with embodiment 10 of the presentinvention is applied to a projection device;

[0033]FIG. 14 is a drawing illustrating an example in which an imagedisplay device in accordance with embodiment 11 of the present inventionis applied to a head-mounted display;

[0034]FIG. 15 is a drawing illustrating a further example in which animage display device in accordance with embodiment 12 of the presentinvention is applied to a projection device; and

[0035]FIG. 16 is a drawing illustrating a conventional optical switchingelement using a liquid crystal.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0036] Embodiments of the present invention will be described below withreference to the drawings.

[0037] The principle of an optical switching element of the presentinvention lies in the characteristic that light is switched by switchinga member comprising a transparent or transmissive extraction surface andprovided opposite to a light guide comprising a glass plate or the likefor transmitting light by total reflection between a first position atan extraction distance of a wavelength or less, preferably half awavelength or less, where the member is brought near or into contactwith the light guide by using electrostatic force or amagnetorestrictive effect to extract leaking evanescent waves, and asecond position where total reflection conditions are not satisfied soas not to output the evanescent waves.

[0038]FIG. 1 shows the schematic configuration of an optical switchingelement 1 in accordance with an embodiment of the present invention.This optical switching element 1 comprises a light guide 21 serving as alight guide body (light guide unit) having high light transmittance andmade of glass or transparent plastic. The light guide 21 has a surface22 and a back 23 which are formed at an appropriate angle for the angleof incidence of incident light 10 so that the incident light 10 istransmitted by total reflection. Irregularity 24 is formed on surface22. The irregularity has an appropriate height and is formed by atechnique such as etching or the like. Transparent electrode 31 having athickness of about 0.1 μ is provided in a groove 25 so that a surface 32of the transparent electrode 31 also serves as a surface (totalreflection surface) for total reflection of the incident light 10. Atransparent thin film 40 of a PET polymer film or an inorganic materialis laminated on the surface 22 of the light guide 21 having theirregularity 24 formed thereon. The lands 26 of the irregularity 24serve as spacers to keep the distance between the thin film 40 and thebottom of the groove 25 constant.

[0039] In the optical switching element 1, an electrostatic thermaljunction (anodic junction) technique is used for connecting the thinfilm 40 and the light guide 21, in which a high potential is applied atan appropriate temperature. Therefore, an additional layer such as anadhesive layer need not be provided at the top 27 of each of the lands26 where the thin film 40 and the light guide 21 are joined together,and thus a gap between the thin film 40 and the bottom of the groove 25can precisely be maintained. A transparent electrode 35 is provided onthe groove-side surface 41 of the thin film 40 so that when potentialswith different polarities are applied to both transparent electrodes 35and 31, the electrodes attract each other by electrostatic force, andthe groove-side surface (extraction surface) 36 of the transparentelectrode 35 is brought near or into contact with the surface 32 (totalreflection surface) of the electrode 31 provided on the groove side toextract light from the light guide 21 by a light extraction unit 50.Namely, in this embodiment, the transparent electrode 35 constitutespart of the light extraction unit 50 and has surface 36 which serves asthe extraction surface. Although the transparent electrodes 35 and 31are provided with a known insulating layer made of silicon oxide ofabout 0.02 μ, which is used for a liquid crystal display device and thelike, detailed description thereof is omitted.

[0040] The light 11 extracted by the extraction surface 36 passesthrough the thin film 40 and an emission optical element (emissionmember) 43 provided on the opposite surface 42 of the thin film 40, andis emitted as outgoing light 12 to the outside. Therefore, in theoptical switching element 1 of this embodiment, the transparentelectrode 35 and the emission member 43 function as the light extractionunit 50. In this embodiment, the emission member 43 comprises atransparent micro prism 44 of a polymer or an inorganic material havinga shape (truncated pyramid) in which the tip of a pyramid is truncated.The micro prism 44 is provided so that the bottom area on the side nearthe light guide 21 is smaller than the area on the opposite side.Therefore, the extracted light 11 guided to the micro prism 44 isreflected by the side 44 a at a different angle from the totalreflection surface, and emitted upward as the outgoing light 12 in thedirection substantially perpendicular to the total reflection surface32, i.e., the outgoing light 12 having a radiation distribution which ismade perpendicular to the surface of the light guide 21.

[0041] It is known that when a transparent body is brought near thetotal reflection surface, evanescent waves leak to the transparent bodyside, and light is transmitted therethrough. FIG. 2 shows an example oftransmittance. Although the transmittance of evanescent waves dependsupon the refractive index of a medium and the angle of incidence, itshows substantially the same tendency, and evanescent waves can beextracted by bringing the transparent body near the total reflectionsurface at a distance of half a wavelength or less therefrom. Since thetransparent electrode 31 which forms the total reflection surface 32 andthe transparent electrode 35 which forms the extraction surface 36 havesubstantially the same refractive index, if these electrodes contactwith each other, incident light passes through the extraction surface 36from the light guide 21 serving as the light guide unit without totalreflection by the total reflection surface 32, and travels as theextracted light 11 to the transparent electrode 35. Thus, the extractedlight 11 can be obtained from the total reflection surface 32 directlyor with the evanescent waves extracted, and thus output as the outgoinglight 12 through the emission optical element 43.

[0042] As described above, it is known that when the transparent bodyhaving the extraction surface formed thereon is brought near the lightguide unit for total reflection at a distance of a wavelength or lesswithout contact therebetween, the evanescent waves leaking to externalair or vacuum from the light guide unit in an amount of about awavelength can be extracted to the transparent body side. The evanescentwaves are light present due to slight penetration of totally reflectedlight from a medium with a high refractive index into a medium with alow refractive index when the phenomenon of total reflection isconsidered on the basis of the wave theory, the light being generallyreturned to the medium with a high refractive index to produce totallyreflected light. In the optical switching element 1 of the presentinvention, since such leaking evanescent waves can also be extracted,the optical switching element sufficiently functions as an opticalswitching element even if the extraction surface 36 is not necessarilyadhered to the total reflection surface 32, and an optical switchingelement having high reliability is realized.

[0043] On the other hand, where the distance between the totalreflection surface 32 and the extraction surface 36 is about half awavelength or more, the transmittance of the evanescent waves becomessubstantially zero, without emission of light. Therefore, a switchingelement with high contrast can be realized. In the optical switchingelement 1 of this embodiment, the distance between the surface 32 of thetransparent electrode 31 on the light guide side, which serves as thetotal reflection surface, and the surface 36 of the transparentelectrode 35 on the thin film side, which serves as the extractionsurface, is set to an appropriate value by controlling the height of thelands 26 serving as spacers. When voltages with different polarities areapplied to both electrodes 31 and 35, both electrodes approach eachother to cause leakage of the evanescent waves (first position). When novoltage is applied or the same potential is applied to both electrodes31 and 35, the electrode surfaces 32 and 36 separate from each other tocause no leakage of the evanescent waves (second position). Therefore,it is necessary to precisely control the thickness of the portion ofjunction between the lands 26 and the thin film 40. From this viewpoint,the use of electrostatic thermal junction eliminates the need for anadhesive layer, and thus permits junction of the light guide 21 and thethin film 40 with high precision.

[0044] As described above, in the optical switching element 1 of thisembodiment, on-off control can be made by controlling the polarities ofthe potentials applied to the transparent electrodes 31 and 35 to emitthe incident light 10 of the light guide 21. The distance of movement ofthe light extraction unit 50 supported by the thin film 40 may be of theorder of half a wavelength, and thus the optical switching element canbe operated at an operational speed of as fast as 10⁻³ to 10⁻⁶ secondsor less. The transmittance of the light guide 21 can be switched fromsubstantially 0% to 100% by moving the light extraction unit 50 forabout a wavelength, and the optical switching element with very highcontrast can be realized. Therefore, the optical switching element 1 ofthis embodiment permits time-division control with high resolution, andfacilitates control of multiple grayscale.

[0045] The optical switching element 1 of this embodiment can bemanufactured by using a semiconductor manufacturing technique or micromachine manufacturing technique which is suitable for fine processing,such as etching and the like, and thus the size of one switching elementcan be from tens to several hundreds μ. Also the optical switchingelement 1 is an integrated element comprising a laminate of the thinfilm 40 and the light guide 21, and can be provided as an activeswitching element as a unit in which the electrodes 31 and 35 fordriving the light extraction unit 50 are integrated. Therefore, it iseasy to integrate a plurality of optical switching elements 1 at highdensity, and possible to realize a thin switching element for imagedisplay having high resolution, as described below in detail.

[0046]FIG. 3 shows an optical switching element in accordance withanother embodiment. The optical switching element 1 of this embodimentalso comprises a light guide 21 having irregularity 24 formed on thesurface thereof, and a thin film 40 laminated thereon. Portions commonto the above portions are denoted by the same reference numerals, andare not described below. Also in each of the embodiments describedbelow, the common portions are denoted by the same reference numerals,and are not described.

[0047] In the optical switching element 1 of this embodiment, astructure is employed as the emission member 43 in which a plurality ofcylindrical or prismatic small transparent bodies 45, having a sectionalarea of several times to several tens of times as large as a wavelength,are arranged. Namely, when potentials with different polarities areapplied to the transparent electrodes 31 and 35 to bring the extractionsurface 36 near or into contact with the total reflection surface 32,the extracted light 11 enters the prismatic or cylindrical transparentbodies 45. The extracted light 11 is applied to the sides of theprismatic or cylindrical transparent bodies 45, and refracted andemitted to the outside or reflected and emitted upward to the outside.Therefore, scattered light can be obtained as the outgoing light 12. Theefficiency of light extraction and the degree of scattering can becontrolled by appropriately selecting the sectional area and the lengthof the cylindrical or prismatic transparent bodies 45.

[0048]FIG. 4 shows an optical switching element in accordance with stillanother embodiment. In the optical switching element 1 of thisembodiment, the micro prism 44 functioning as the emission member 43 isprovided on the lower side of the transparent thin film 40 which facesthe light guide 21, i.e., on the extraction side thereof, and thetransparent electrode 35 is provided at the top (the light guide side)44 b of the micro prism 44. Therefore, when a potential difference isapplied to the electrodes 35 and 31 to bring the extraction surface 36near or into contact with the total reflection surface 31, the incidentlight 10 propagating under total reflection by the light guide 21 isextracted when passing through the transparent electrode 35 and themicro prism 44 which constitute the extraction unit 50. The extractedlight 11 is reflected by the side 44a of the micro prism 44 and emittedas the outgoing light 12 through the thin film 40 in the directionsubstantially perpendicular to the light guide 21.

[0049] Although the emission member 43 can be disposed between the thinfilm 40 and the groove 25 to form the optical switching element 1, as inthis embodiment, the difference in height of the irregularity 24 formedon the surface 22 of the light guide 21 must be increased. Therefore, itis difficult to maintain the processing precision of the light guide 21.However, since the emission side of the optical switching element 1 iscovered with the thin film 40, the optical switching element 1 providesthe advantage that it can be superimposed on another optical device.Also since the transparent electrode 35 is provided on the light guideside of the emission member 43; if the distance between the thin film 40and the bottom of the groove 25 is increased, the distance between thetransparent electrodes 35 and 31 is not increased. Therefore, thedistance between the electrodes 35 an 31 is small; the optical switchingelement 1 can be driven with a low driving voltage, and powerconsumption (operation power) can be decreased.

[0050]FIG. 5 shows an optical switching element 1 in accordance with afurther embodiment. Each of the above optical switching elements 1comprises the transmissive light extraction unit 50 which reflects orrefracts the extracted light 11 at appropriate gentle angles toward theupper portion of the drawing, i.e, the surface 22 of the light guide 21on the emission side, to emit the light upward, and which is supportedby the transparent thin film 40 on the emission side of the light guide21. However, the optical switching element 1 of this embodimentcomprises the reflective light extraction unit 50 which reflects atsharp angles the extracted light 11 extracted toward the lower side 23(the side opposite to the emission side, i.e., the back side) of thelight guide 21, and guides the outgoing light 12 upward to the emissionside. The reflective light extraction unit 50 is supported by an opaqueor reflective thin film 49 on the back side 23 of the light guide 21.

[0051] In the optical switching element 1 of this embodiment, theboron-doped silicon thin film 49 which can be thinned by etching isused, and laminated on the lands 27 formed on the back side 23 of thelight guide 21 by electrostatic thermal junction. On the lightguide-side surface 41 of the thin film 49 of the reflective lightextraction unit 50 are laminated the transparent electrode 35, theemission member 43 containing a light scattering material 48, and analuminum layer 51 as a reflecting film from the back side of the lightguide 21.

[0052] Therefore, when potentials with different polarities are appliedbetween the electrodes 31 and 35, the extraction surface 36 is broughtnear or into contact with the total reflection surface 32 to obtain theextracted light 11, as in each of the above optical switching elements.In the optical switching element 1 of this embodiment, the extractedlight 11 is scattered in the emission member 43 containing thescattering material 48, and the outgoing light 12 scattered upward inthe emission direction travels upward, passes through the light guide21, and is emitted from the surface 22 of the light guide 21. Theoutgoing light 12 scattered downward is reflected upward in the emissiondirection by the aluminum reflecting film 51, and emitted through thelight guide 21.

[0053] The optical switching element I of this embodiment can be formedby using the reflective light extraction unit 50 so that light can beemitted from the light guide 21, as in this embodiment. In this type ofoptical switching element, since light is emitted from the surface 22 ofthe light guide 21, another optical element such as a lens or the likecan easily be disposed on the surface side. Also the use of the opaqueboron-doped silicon thin film 49 can prevent entrance of extraneouslight as a noise, and permits optical switching with high contrast.Further, even in the optical switching element 1 of this embodiment, thetransparent electrode 35 is provided on the light guide-side of theemission member 43 containing the scattering material to minimize thedistance between both electrodes 31 and 35 so that the optical switchingelement 1 can be driven at a high speed with low driving voltage.

[0054] As the scattering material 48 contained in the emission member43, a dye having wavelength selectivity can be used. In this case, onlylight at a specified wavelength can be emitted by providing anabsorptive film in place of the reflecting film, resulting in therealization of an optical switching element which enables color display.

[0055]FIG. 6 shows an optical switching element I in accordance with astill further embodiment of the present invention. The optical switchingelement 1 of this embodiment comprises the reflective light extractionunit 50, but, in this embodiment, the reflective emission member 43comprising the micro prism 44 or the like is provided on the outside 42of the transmissive thin film 40. The reflective light extraction unit50 can be formed by using the transmissive thin film 40, as in thisembodiment. Also the light extraction unit 50 can be provided on theback side 23 of the light guide 21 to guide the outgoing light 12 to theback side 23 of the light guide 21. Further, an optical element havingwavelength selectivity, such as a dichroic prism or the like, can beused as the micro prism 44 to provide an optical switching elementcapable of color display.

[0056]FIG. 7 shows an optical switching element 1 in accordance with afurther embodiment of the present invention. The optical switchingelement 1 of this embodiment comprises the reflective light extractionunit 50, and employs the electrostrictive force caused by a piezoelement 59 in place of electrostatic force caused by electrodes as amechanism for driving the light extraction unit 50. The piezo element 59of this embodiment is a bimorph type in which two layers havingdifferent polarization directions are laminated, so that when apotential is applied, the piezo element 59 is curved to press the lightextraction unit 50 toward the light guide 21 by the force of curvature.

[0057] In the optical switching element 1 of this embodiment, the lightextraction unit 50 comprising the emission member 43 containing thescattering material 48 is supported by the boron-doped silicon thin film49. When the piezo element 59 is curved to press the emission member 43toward the light guide 21, the surface 43 a of the emission member 43contacts or approaches, as the extraction surface, the back side 23 ofthe light guide 21 for transmitting light by total reflection, and theincident light 10 is guided as the extracted light 11 to the emissionmember 43. The outgoing light 12 scattered in the emission member 43passes through the light guide 21 and is emitted from the surface 22 ofthe light guide 21. Of course, the aluminum reflecting layer-51 may beprovided between the emission member 43 and the thin film 49.

[0058] As described above, the optical switching element 1 of thisembodiment can be driven by using a driving force other thanelectrostatic force. However, from the viewpoints of support andarrangement of the piezo element 59 as a driving member and power supplydevice, the use of electrostatic force caused by the electrodes cansimplify the configuration, and facilitates formation of the opticalswitching element 1 as a unit.

[0059] Also where a plurality of light extraction units are assembled,of course, the light extraction units 50 can be assembled as movableunits separated from the light guide 21 as the light guide unit.However, as shown in the above embodiments, the light extraction unit 50is attached to the thin film 40 or 49, and the thin film is laminated onthe surface of the light guide 21 having the irregularity 24 formedthereon, thereby simplifying unitization and maintaining an appropriatedistance between the light extraction unit 50 and the light guide 21with the lands 26 of the irregularity 24 as spacers therebetween.Therefore, it is possible to provide at low cost an optical switchingelement with high contrast and high performance which can be operated athigh speed in accordance with the present invention.

[0060]FIG. 8 shows an optical switching element 1 in accordance with afurther embodiment of the present invention. The optical switchingelement 1 of this embodiment comprises a substantially spherical microlens 46 serving as the emission member 43. By using the micro lenshaving a shape closer to a sphere rather than a semisphere as theemission member, it is possible to correct the direction of the outgoinglight 12 by refraction, and efficiently extract the light from the lightguide to the outside thereof.

[0061] Further, in the optical switching element 1 of this embodiment,fused quartz which efficiently transmits ultraviolet rays having awavelength of approximately 160 nm is used as the light guide 21 so thatultraviolet light is incident as the incident light 10 from a blacklight (ultraviolet light source). The emission member 43 contains afluorescent agent 47 which emits fluorescence by ultraviolet light, sothat the emission member 43 emits light as the outgoing light 12 by theextracted light 11. Namely, in the optical switching element 1 of thisembodiment, the energy of ultraviolet light transmitted through thelight guide 21 is extracted through the extraction surface 36, convertedinto visible light by the emission member and output. By selecting anappropriate material as the fluorescent material 47, color display canbe realized by using ultraviolet light in the light extraction unit 50.As the fluorescent material, (Y, Gd)BO₃:Eu³⁺which emits red light,BaAl₁₂,P₉:Mn which emits green light, and BaMgAl₁₄O₂₃:Eu²⁺which emitsblue light can be used. Grayscale made by using the optical switchingelement which can emit light of these primary colors permitshigh-resolution full color display.

[0062] In this embodiment, a light absorbing layer 29 is formed on theback side 23 of the light guide 21 so as to prevent entrance of lightfrom the outside, thereby obtaining fluorescence with high contrast.

[0063] As described above, the optical switching element 1 of thisembodiment comprises a self light emission type light extraction unit50. However, scattering agent 48 can be contained in the emission member43 in place of the fluorescent material 47 to provide a direct-sighttype optical switching element comprising a scattering type lightextraction unit, in which visible light is supplied to the light guide21. Of course, it is possible to provide an optical switching element inwhich the incident light 10 is extracted and emitted by the transparentmicro lens 46 having a shape close to a sphere.

[0064]FIG. 9 shows an optical switching element 1 in accordance with afurther embodiment of the present invention. Although, in each of theabove-described optical switching elements 1, the light extraction unit50 comprises the emission member 43 so that the emission member 43 ismoved with movement of the extraction surface, the optical switchingelement 1 of this embodiment comprises a light processing unit 60 notdriven by the thin film 40 and provided on the emission side where theextracted light 11 extracted from the light guide 21 is emitted so thatthe extracted light 11 is processed (converted) to the outgoing light 12by the light processing unit 60. The light extraction unit 50 of thisembodiment only functions to extracted light 11 from the light guide 21,and can be formed in a very simple structure in which micro prisms aremounted to form a surface which causes no total reflection. Therefore,it is possible to significantly decrease the load for driving the lightextraction unit 50, and provide an optical switching element which canbe operated at a high speed with low power consumption and is capable ofexpressing multiple grayscale.

[0065] The light processing unit 60 can be formed separately from thelight extraction unit 90 and can thus be provided with variousfunctions. For example, the function as a micro lens for increasing thedirectivity of the outgoing light 12 can be imparted to provide awavefront converting function. Since the light processing unit 60 can beprovided separately from the light extraction unit 50, the lightprocessing unit 60 having sufficient curvature can be provided. Alsowavelength selectivity can be imparted by mixing the scattering material48 which scatters a specified wavelength. Since movability need not betaken into consideration, the light processing unit 60 containing asufficient amount of scattering material 48 can be provided. Of course,the light processing unit 60 containing a luminescent agent such as afluorescent agent can be set so that light other than visible light suchas ultraviolet light and the like can be processed. Further, the lightprocessing unit 60 having a plurality of functions can be laminated sothat the light 11 extracted from the light guide 21 can be appropriatelyprocessed and then emitted.

[0066] As described above in the optical switching elements inaccordance with the embodiments of the present invention, in the opticalswitching element of the present invention, the totally reflectedincident light is extracted and emitted, thereby causing less loss oflight due to the polarizer, and efficiently extracting the incidentlight. Also since the distance of movement of the light extraction unitfor turning on and off is as small as the unit of a wavelength or half awavelength, it is possible to achieve high speed response and highcontrast. Further, the optical switching element of the presentinvention can be manufactured by a general manufacturing method as asemiconductor manufacturing method or micro machine manufacturingmethod, such as etching or the like, and can thus be simply manufacturedand provided in high yield and at low cost. Therefore, by arranging theoptical switching elements of the present invention in a two-dimensionalform, it is possible to provide an image display device capable of colordisplay with high resolution. Some examples of such image displaydevices are described below. The portions which have been describedabove are denoted by the same reference numerals and are not describedbelow.

[0067]FIG. 10 shows a state wherein an image is projected by using animage display device 2 of the present invention. The light emitted froma lamp 5 as a light source travels as the incident light 10 through thelight guide 21 of the image display device 2 under total reflection, andreaches an optical switching unit 3 comprising a plurality of lightextraction units 50 arranged in a two-dimensional form. In the lightextraction units 50.arranged in a two-dimensional form, the light isextracted in a portion to which a voltage is applied, and emitted as theoutgoing light 12. The outgoing light 12 is converged by a projectionlens 6 and projected on a screen 7.

[0068]FIG. 11 shows the optical switching unit 3 of the image displaydevice 2 in accordance with an embodiment of the present invention. Theoptical switching unit 3 of this embodiment has a structure in whichmany switching elements of embodiment 1 are arranged in atwo-dimensional form. In the switching unit 3 of this embodiment, theoptical switching elements respectively comprising the microprism 44serving as the emission members 43, which constitute the lightextraction units 50, a prism 44R having wavelength selectivity totransmit red light, a prism 44G having wavelength selectivity totransmit green light, and a prism 44B having wavelength selectivity totransmit blue light are arranged in order to permit full color displayin one pixel comprising a group of these three optical switchingelements.

[0069] In the switching unit 3 of this embodiment, grayshading can bemade by adjusting the application time of the voltage applied to theelectrodes 31 and 35 of each of the optical switching elements 1. Ingray tone display as an example, black is not extracted from the lightguide 21 because the application time is zero, while white is extractedfor the longest time because of the minimum application time.Intermediate grayscale can be expressed by adjusting the applicationtime. Such grayscale control is performed for each of the switchingelements respectively comprising the prisms 44R, 44G and 44B for thethree colors to achieve full color display. Further, since the switchingelements of the present invention can be driven at high speed, andmultiple grayshading can be achieved, full color expression with highresolution can be made.

[0070] Besides the micro prism 44, the wavelength selectivity may berealized by providing a color filter near other portions through whichlight is transmitted, e.g., the transparent electrodes 35. Also thewavelength selectivity may be realized by manufacturing the micro prism44 comprising a dye dispersed in a transparent resin, or forming adichroic mirror comprising a dielectric multi-layered film near thetransparent electrodes. In this way, various methods can be used.

[0071]FIG. 12 shows a schematic configuration of the switching unit 3 ofthe image display device 2 of the present invention, with the thin film40 partially cut away. The switching unit 3 of this embodiment comprisesthe switching elements 1 arranged in a two-dimensional form. Therefore,the transparent electrodes 31 extending in the scanning direction arearranged at the predetermined pitch in the light guide 21, and thetransparent electrodes 31 extending in the sub-scanning directionperpendicular to the scanning direction are arranged at thepredetermined pitch. The scanning direction and the sub-scanningdirection may be reversed. The micro prisms 44 serving as the emissionmembers 43 are provided at the intersections of the transparentelectrodes 31 and 35 to form the optical switching elements I eachcomprising the light extraction unit 50. In this embodiment, the lands(projections) 26 for supporting the thin film 40 are formed in aprismatic shape around each of the optical switching elements 1 tosupport each of the light extraction units 50 at four positions around,the lands 26 being strongly joined to the thin film 40 by a method suchas electrostatic thermal junction without interference with theelectrodes 35. Since each of the movable light extraction units 50 issupported at four positions around, it is possible to secure a wide areafor the extraction surface (the surface of each electrode 35) in contactwith the surface 32 of each of the transparent electrodes as the totalreflection surface. Therefore, it is possible to obtain the extractedlight with high intensity from the light guide 21 in each of the lightextraction units 50, and form the image display device 2 capable ofdisplaying a bright image.

[0072]FIG. 13 shows an image display device in accordance with anotherembodiment of the present invention. The image display device 2 of thisembodiment comprises the prismatic light guide 21 so that the incidentlight 10 from the light source 5 is applied directly to the totalreflection surfaces of the optical switching unit 3. The use of such animage display device 2 eliminates the need for setting the direction ofthe incident light 10 to be perpendicular to the emission direction.Therefore, in an applied apparatus comprising the light source 5 and theimage display device 2, such as a projector or the like, the directionof the light source 5 and the image display device 2 can be set at anappropriate angle, and thus a compact projector or the like conformingto the operation state can be provided.

[0073]FIG. 14 shows the use of an image display device in accordancewith an embodiment of the present invention. In this embodiment, theimage display device 2 is applied to a head-mounted display. The lightemitted from LED 70 serving as a light source enters as the incidentlight 10 a prism 71 mounted on the light guide 21 of the image displaydevice 2, and travels through the light guide 21 under total reflection.The light 10 is switched by the optical switching unit 3 to form animage which reaches the eye 73 through a converging lens 72. In thisembodiment, the optical switching unit 3 comprises a scattering typelight extraction unit suitable for direct vision, for example, the lightextraction unit described above in embodiment 2.

[0074] The LED 70 as the light source for the image display device 2comprises three types of LED 70 a, 70 b and 70 c which can emit light ofthe primary colors such as red, green and blue, or cyan, magenta andyellow so that time-division luminescence of each of the LEDs causesincidence of light of the corresponding color on the image displaydevice 2. Therefore, in the switching unit 3 of the image display device2, the optical switching elements for displaying respective dots arerespectively operated to express the colors in synchronism with thetimes of luminescence of the LED 70 a, 70 b and 70 c, to display a fullcolor image.

[0075] It is also possible to provide an image display device forhead-mounted display capable of full color display by using a scatteringtype light extraction unit with wavelength selectivity, e.g., theoptical switching element described in embodiment 4, 6 or 8. Where thelight extraction unit having wavelength selectivity is used, a whitelight source can be selected as the light source. Therefore, an imagecan be displayed by incidence of external light in which the directivityis controlled by using an appropriate optical system. An image displaydevice capable of displaying a color image by using an optical switchingelement comprising an emissive light extraction unit, as described inembodiment 7, can also be provided. embodiment 12

[0076]FIG. 15 shows a projection type image display device in accordancewith another embodiment of the present invention. Although, inembodiments 10 and 11, the optical switching element comprising thetransmissive light extraction unit is used, the switching unit 3 of theimage display device 2 of this embodiment comprises reflective lightextraction units. For example, the optical switching element describedin embodiment 5 can be used. In this embodiment, the light guide 21 ofthe image display device 2 has an incident surface 81 on which light ofthe primary colors such as red, green and blue (RGB), or cyan, magentaand yellow are incident from a light source in a time vision manner. Inthis embodiment, the light source 80 comprises a white metal halide lamp80 a, and a three color division filter 80 b rotated by a motor so thatlight subjected to color division by the three color division filter 80b is converged through a collimator lens 80 c to form a parallel lightflux which is incident on the incident surface 81 of the light guide 21.The incident light 10 reaching the optical switching unit 3 is reflectedby the optical switching elements, passes through the light guide 21 andis emitted as the outgoing light 12 to form an image on a screen througha projection lens 85. On the other hand, part of the incident light notconverted into the outgoing light by the optical switching elements ofthe optical switching unit 3 reaches a reflection surface 82 of thelight guide 21 on the side opposite to the incident surface 81 by totalreflection, is reflected by the reflection surface 82, again transmittedthrough the light guide 21 and reaches the optical switching unit 3.

[0077] In this way, the image display device 2 of this embodiment canproject a color image by operating the optical switching unit 3synchronously with the incident light subjected to time division. Likein the above-described image display device comprising the transmissiveoptical switching unit, a color image can also be displayed by theoptical switching unit 3 comprising the light extraction units withwavelength selectivity using white light as the incident light 10.

[0078] The above-mentioned optical switching elements and image displaydevices are only embodiments of the present invention, and of course thepresent invention is not limited to these embodiments. The opticalswitching element of the present invention can also be applied toapparatus other than those discussed above, which use a laser as amonochrome light source. The application of the optical switchingelement of the present invention is not limited to the image displaydevice, and the optical switching element can be widely applied to alinear light valve for a light printer, a light space modulator forthree-dimensional hologram memory, and the like. The optical switchingelement of the present invention is particularly suitable for not onlythe field of application of conventional optical switching elementscomprising a liquid crystal, but also fields and applied apparatus inwhich an optical switching element comprising a liquid crystal exhibitsan insufficient operational speed and light intensity. Further, theoptical switching element of the present invention can be finelyprocessed and can thus be made small and thin, as compared with aconventional optical switching element comprising a liquid crystal, andhigher integration can also be attained.

[0079] As described above, in the optical switching element of thepresent invention, the lightweight extraction unit can be operated as amovable unit in a movement range of as small as approximately awavelength or less to extract light sealed by total reflection. Thus, aresponse speed of 1 millisecond or less can be obtained, and when theswitch is turned off by separating the light extraction unit from thetotal reflection surface, no light is output because of total reflectionof light. It is thus possible to obtain an optical switching elementhaving very high contrast. In addition, not needing for a polarizerenables a decrease in light loss, and the optical system forillumination can be made small and thin.

[0080] As the emission member for emitting the extracted light, variousstructures can be used, as described above. For example, by using amicro prism or micro lens, the outgoing light can efficiently beemitted. By using a transparent body having a shape in which the tip ofa substantially cone or pyramid is truncated, and the bottom area nearthe light guide is smaller than that on the opposite side, it ispossible to increase the emission efficiency and control the directionof the outgoing light in a predetermined direction.

[0081] Further, when the light extraction unit is supported by a thinfilm which is laminated on the light guide, and a structure forgenerating electrostatic force is used as a mechanism for driving thelight extraction unit, an integrated optical switching element caneasily be constructed and manufactured by a thin film technique, andmicro machine technique. Therefore, a small, thin optical switchingelement with higher reliability can be provided at low cost.

[0082] Also the optical switching elements of the present invention canbe arranged in a two-dimensional form for image display. Since no lightis emitted due to total reflection when the optical switching elementsare turned off, an image display device with high contrast can beprovided. Further, grayscale can be expressed by controlling theapplication time of a voltage in the optical switching elements of thepresent invention which have a high operational speed, and thusgrayscale with higher precision than grayscale expressed by controllingthe voltage level in a liquid crystal display or the like can berealized by digital signal processing. Further, since the opticalswitching element can be utilized by guiding light into the light guide,the illumination optical system of the image display device of thepresent invention can be simplified, and the image display device can beapplied to various apparatus such as a projector and head-mounteddisplay having a simple configuration.

[0083] Also a full color display can be made by imparting wavelengthselectivity to the light extraction unit or supplying, as incidentlight, light of the primary colors subjected to time division. Since theoptical switching element of the present invention permits emission oflight with high intensity, high-speed operation and multiple grayscalecontrol, an image display device capable of high-quality color displaycan be provided.

What is claimed is:
 1. An optical switching element, comprising: a lightguide unit having a total reflection surface that can transmit light bytotal reflection; and a light extraction unit having a transmissiveextraction surface, the transmissive extraction surface being movablebetween a first position at or less than an extraction distance from thetotal reflection surface such that an evanescent wave can leak, and asecond position greater than the extraction distance from the totalreflection surface.
 2. The optical switching element according to claim1, the light extraction unit further comprising an emission member thatemits light extracted by the transmissive extraction surface.
 3. Theoptical switching element according to claim 2, the emission membercomprising at least one of an emission surface and a reflection surfacewhich is disposed at an angle relative to the total reflection surface.4. The optical switching element according to claim 2, the emissionmember comprising at least one of a micro prism and a micro lens.
 5. Theoptical switching element according to claim 2, the emission membercomprising an optical element shaped as at least one of a truncated coneand a truncated pyramid which expands in an emission direction.
 6. Theoptical switching element according to claim 2, the emission memberhaving a light scattering ability.
 7. The optical switching elementaccording to claim 2, the emission member emitting light by theextracted light.
 8. The optical switching element according to claim 7,the emission member including a fluorescent agent.
 9. The opticalswitching element according to claim 1, the light extraction unit havingwavelength selectivity.
 10. The optical switching element according toclaim 1, the light extraction unit being of a transmission type whichguides extracted light in a direction opposite to the transmissiveextraction surface, the light extraction unit being provided on anemission side of the optical switching element relative to the lightguide unit.
 11. The optical switching element according to claim 1, thelight extraction unit being a reflection type which guides extractedlight to the transmissive extraction surface, the light extraction unitbeing provided on a side opposite to an emission side of the opticalswitching element relative to the light guide unit.
 12. The opticalswitching element according to claim 1, the light extraction unit beingof at least one of a scattering type which scatters extracted lightextracted by the transmissive extraction surface, and an emission typewhich emits light by extracted light, and a light absorbing layer isdisposed on a side opposite to an emission side of the optical switchingelement relative to the light guide unit.
 13. The optical switchingelement according to claim 1, further comprising a static lightprocessing unit provided on an emission side of the optical switchingelement where extracted light extracted by the light extraction unit isemitted.
 14. The optical switching element according to claim 13, thelight processing unit having a wavefront converting function.
 15. Theoptical switching element according to claim 13, the light processingunit having a wavelength selecting function.
 16. The optical switchingelement according to claim 13, the light processing unit having at leastone of a scattering and light emitting function.
 17. The opticalswitching element according to claim 1, further comprising a spacer anda thin film laminated on the light guide unit via the spacer so that thelight extraction unit is supported by the thin film.
 18. The opticalswitching element according to claim 10, further comprising a spacer anda transmissive thin film laminated on the emission side of the optionalswitching element relative to the light guide via the spacer so that thelight extraction unit is supported by the transmissive thin film. 19.The optical switching element according to claim 11, further comprisinga spacer and a reflective thin film laminated on the side opposite tothe emission side of the optical switching element relative to the lightguide via the spacer so that the light extraction unit is supported bythe reflective thin film.
 20. The optical switching element according toclaim 17, further comprising a driving unit that can drive the lightextraction unit supported by the thin film.
 21. The optical switchingelement according to claim 20, the driving unit being capable ofelectrostatically driving the light extraction unit.
 22. The opticalswitching element according to claim 21, further comprising atransparent electrode provided on the total reflection surface.
 23. Theoptical switching element according to claim 21, the light extractionunit further comprising an emission member that emits light extracted bythe transmissive extraction surface, and a transparent electrode isprovided on a light guide side of the emission member.
 24. The opticalswitching element according to claim 21, the spacer having a prismaticshape for supporting the light extraction unit at each of fourpositions.
 25. The optical switching element according to claim 21, thethin film being joined to the spacer by electrostatic thermal junction.26. An image display device comprising a plurality of optical switchingelements, each of the optical switching elements having a structureaccording to claim 1, the optical switching elements being disposed in atwo-dimensional form, the light guide unit of each of the opticalswitching elements being connected to transmit light.
 27. The imagedisplay device according to claim 26, further comprising a spacer and athin film laminated on the light guide unit of each of the opticalswitching elements via the spacer, for supporting the light extractionunit of each of the optical switching elements.
 28. The image displaydevice according to claim 27, the spacer having a prismatic shape forsupporting the light extraction unit of each of the optical switchingelements at each of four positions.
 29. The image display deviceaccording to claim 27, the thin film being joined to the spacer byelectrostatic thermal junction.
 30. The image display device accordingto claim 27, further comprising a driving unit that can drive the lightextraction unit of each of the optical switching elements supported bythe thin film.
 31. The image display device according to claim 30, thedriving unit comprising a scanning electrode and a sub-scanningelectrode perpendicular to the scanning electrode so that at least oneof the scanning electrode and the sub-scanning electrode is disposed onthe light guide unit of at least one of the optical switching elements,the other being disposed on at least one of the thin film and the lightextraction unit of each of the optical switching elements.
 32. The imagedisplay device according to claim 31, wherein the at least one of thescanning electrode and the sub-scanning electrode provided on the lightguide unit is a transparent electrode.
 33. The image display deviceaccording to claim 27, each of the light extraction units havingwavelength selectivity.
 34. The image display device according to claim27, further comprising a light source that can supply light of primarycolors to the light guide unit of each of the optical switching elementsin a time division manner.
 35. A method of manipulating light,comprising the step of: moving a transmissive extraction surface of alight extraction unit between a first position at or less than anextraction distance from a total reflection surface of a light guideunit such that evanescent light can leak, and a second position greaterthan the extraction distance from the total reflection surface.
 36. Themethod according to claim 35, further comprising the step of emittinglight extracted by the transmissive extraction surface with an emissionmember of the light extraction unit.